The present invention generally relates to industrial material handling. More particularly, the present invention relates to a unique handling assembly for precisely orienting and fixturing an array of wet contact lenses between manufacturing processing stations to facilitate the automated handling thereof Although the invention is described and shown herein as directed toward contact lens manufacturing, it is understood that the invention may be used to orient and fixture other, similarly shaped work pieces (e.g., intraocular lenses).
Contact lens manufacturing, especially soft contact lens molding manufacturing, has become a very automated process in recent years, although there still remains points along some manufacturing platforms requiring direct human handling of the individual lenses. Human handling of contact lenses in a manufacturing line is extremely labor intensive and prone to worker injury in the nature of carpel tunnel syndrome, for example. It is therefore desirable to remove, to the fullest extent possible, direct contact lens handling by workers in a manufacturing facility and replace the manual handling step involved with automated apparatus and methods.
Contact lenses are small, fragile articles of manufacture which require precise optical surfaces. As such, contact lenses are extremely susceptible to scratching and tearing. It is therefore desirable to minimize occurrences of direct touching of the lenses with machine parts. In order to apply automated machinery and methods to contact lens handling, the lenses themselves must be precisely located and fixtured as they travel from one processing station to the next so that the automated machinery can locate and pick the lenses. Should the lenses be shifted slightly and/or oriented differently from their intended locations and orientations, the automated handling will fail and therefore add significantly to the manufacturing operation. Fixturing contact lenses through the various processing stations in a contact lens manufacturing line is a very difficult process to control with the precision required of automation machinery.
Cast molding of contact lenses is known. See, for example, U.S. Pat. No. 5,466,147 issued to Bausch and Lomb Incorporated, the entire reference of which is incorporated herein by reference. A single mold unit comprises a female mold section having a concave optical surface and a male mold section having a convex optical surface. The female and male mold sections are complimentary shaped and mateable to form a lens-molding cavity between the facing concave and convex optical surfaces of the female and male mold sections, respectively.
The basic process for cast molding a lens is as follows. A quantity of liquid lens material (monomer) is dispensed into the concave optical surface of the female mold section and the male mold section is seated upon the female mold section with the concave and convex surfaces thereof facing one another to form a lens-shaped mold cavity. The joined female and male mold sections form a single mold unit which is subject to a curing cycle (e.g., by thermal or UV radiation) thereby causing polymerization of the lens material in the mold cavity. Once the lens material has cured, the male and female mold sections must be separated to retrieve the cured lens.
The opening or release of the mold sections must be carried out in a manner which will not harm the delicate lens. Once the lens has polymerized in the mold cavity, the lens and any lens flash will have an adhesive bond to the opposite concave and convex mold surfaces. Thus, the release of the male mold section from the female mold section must be of a force strong enough to break the adhesive bond of the lens and lens flash to the opposing mold surfaces, yet not so strong or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the mold release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs.
Once the mold sections have been separated, the lens must be released from the mold section on which it is retained. Both wet and dry release methods of lens release have been proposed in the prior art. In wet lens release methods, an aqueous solution is used to wet the hydrophilic lens which absorbs water and swells, causing the lens to separate from the mold surface. Once the lens has hydrated and released from its associated mold surface, the lens becomes a free-floating body in the hydrating fluid. If this process is carried out in a bath, there must thus be some means to contain the hydrated lens, yet not inhibit the access of the hydrating fluid to the interior of the mold and lens. Otherwise, the lenses must be manually xe2x80x9cfished outxe2x80x9d from the hydration bath using tweezers, a very labor intensive prospect.
Typically, the molds in which the lenses have been cured are carried on a support tray in a predetermined array. Once the molds have been opened, the mold sections carrying the adhered lenses are transferred to a lens release station as discussed above. Once the lens has been released form the mold in which it is carried, the lenses are readied for further processing (e.g., hydration, extraction and plasma treatment).
It is desirable to be able to batch process contact lenses through the different stations of a manufacturing process for efficiencies of manufacturing. It is thus desirable to be able to fluid process contact lenses in batches. Various methods of batch processing contact lenses through a fluid processing step have been proposed. The handling of the lenses during fluid processing include processes where the lenses are still in the mold or, alternatively, the lenses have been transferred to a different receptacle. It is furthermore known to use a bath process where batches of lenses may be submerged in a bath of fluid. It is also known to use sequential baths to ensure adequate fluid processing of the lenses. Alternatively, fluid may be applied to each individual contact in metered amounts, followed by extraction of the fluid from the mold section without disturbing the lens.
An example of bath hydration may be seen in commonly owned, co-pending UK application no. 0007930.1 filed on Mar. 31, 2000. In this method, a pallet containing an array of female mold section having respective lenses adhered thereto is stacked on a pallet having a like array of empty male mold sections thereon. An empty pallet is stacked upon the female pallet to prevent the female mold sections from falling from the female pallet during hydration. The stack of three pallets form a single unit for bath hydration, although multiple units may be stacked together and placed in a carrier for submerging in the bath. The pallets are cooperatively configured such that the female and male mold sections are spaced by an amount sufficient to allow fluid to enter between the facing sections to reach the lens, but spaced small enough so as to prohibit the hydrated, loose lens from escaping from between the respective female and male mold sections. This method is especially geared toward a manufacturing method where the male mold section is used for packaging of the contact lens as seen in U.S. Pat. No. 5,537,108 which is of common ownership with the instant application for patent.
In the case where the lenses must be transferred from the mold in which they were formed to a separate package for downstream processes (e.g., hydration and inspection) and/or for final packaging to the consumer (e.g., transfer to a blister package), the lenses must undergo some amount of handling to effectuate this transfer process. In prior art methods, lenses have been transferred manually by an operator using a pair of tweezers to grasp the lens and transfer it from the mold to a package receptacle. This, of course, is an extremely labor intensive method of lens handling and also creates a high chance of lens damage caused by the direct contact with the tweezers and the operator""s inability to consistently control the amount of force used with the tweezers when handling a lens. The use of pick-and place units is also known for transferring lenses between stations, however, this must also be carried out with extreme precision so as to not damage or dislocate the lens during transfer.
It is thus clear that lens handling is a critical parameter in the contact lens manufacturing line. Since contact lenses are extremely delicate, small articles of manufacture having precise optical surfaces, they must be handled with extreme care so as to not damage the lens which increases costs to the manufacturing operation. It is thus an object of a contact lens manufacturing line to use a contact lens handling system which minimizes the amount of direct contact of the handling apparatus with the lenses, yet also achieves consistent lens positioning and location to enable a robust, automated handling process.
The present invention provides an assembly and method for precisely orienting and positioning an array of contact lenses in respective receptacles of a support tray. With the lenses in known positions and orientations on the support tray, they may be further easily handled by a robotic assembly.
Once lenses have been molded and the molds have been opened, the lenses are hydrated and presented in a suitable carrier for the lens positioning station of the present invention. The invention utilizes an array of tubes which are removably mounted upon the first lens support tray with each tube aligning with a respective receptacle and lens on the first support tray. At this point, the lenses are not in a precise location within their respective receptacles on the first support tray. A second, lens-centering tray having an array of lens receptacles is removably mounted to the end of the tubes opposite the first support tray with the receptacles thereof also aligning with the tubes. The assembly comprising the lens trays and tubes is then rotated 180xc2x0 such that the first support tray with lenses thereon is now above the tubes and the lens-centering tray is beneath the tubes. The assembly is then completely submerged into a fluid bath. The fluid passes through openings provided in the lens-centering tray which fills the tubes with fluid, eventually reaching the lenses in the first support tray at the top of the tubes. Once the lenses are submerged in the fluid, the lenses release from their respective receptacles in the support tray and float downwardly through their respective tubes to the lens-centering tray. Due to the curvature of the concave-convex lenses, the lenses will automatically flip as they float downwardly such that they all settle in the concave side-up position within their respective receptacles in the lens-centering tray.
Once all the lenses have settled on the lens-centering tray, the assembly is raised from the fluid bath. A vaccuum source attached to the second support tray is activiated which holds each lens within its respective receptacle in the second support tray. With the tubes guiding the lens downwardly to a respective receptacle, the lenses all settle in a precisely centered location within a respective receptacle. As such, it is then a simple matter for a robotic assembly to pick each lens from its respective receptacle for transfer to another processing station.